The invention relates to a pneumatically-operated machine for spreading granular material, such as seed, fertilizer, or the like, with a metering unit connected to a storage tank and fitted with an inlet hopper, with a rotating annular receptacle for the material to be metered, with stationary deflecting walls leading to discharge apertures and a central opening communicating with an air-line, with an ejector unit connected to the metering unit and opening into the feed for the metered material, through which the said material is passed to the actual spreaders.
Devices of this kind are described, for example, in German Auslegeschrift No. 22 41 534. In this known unit, the ejector unit is arranged in such a manner that it feeds the material released from the metering receptacle upwardly, i.e. a main distributor is arranged above the said ejector unit which passes the material metered by the metering unit to the sub-distributors.
German Auslegeschrift No. 20 25 039 describes and illustrates a general arrangement of this kind, namely a pnuematically-operated machine for distributing granular substances. In this case, frames are located on each side of the central part of the machine. These frames carry not only distributor nozzles, seed shares, seed drills and the like but also sub-distributors distributed uniformly along the length of the said frames.
The purpose of the device according to German Auslegeschrift No. 22 41 534 was to make it possible, on the one hand, to build wide, light-weight machines which could distribute a wide strip of the widest variety of metered substances in a single pass across a field, although the metering had to be carried out with a single mechanism in order to reduce the expense of manufacturing and using such complex and costly metering devices and, on the other hand, to feed this metering unit from a centrally located storage tank divided into different receptacles.
The purpose of the device according to German Auslegeschrift No. 20 25 039 was to provide a machine suitable for spreading wide strips which would overcome the problems associated with the great width of the machine.
In the case of a device according to German Auslegeschrift 20 25 039, the width of the machine is limited in that if only a single, centrally-located metering device, fed from a single storage tank, is to be provided, the efficiency of the pneumatic system and its ability to provide a feed are limited. It must also be taken into account, in this connection that, in the known devices, a rebound plate is arranged in the so-called main distributor above the metering unit, from which hoses run to the various sub-distributors. Now if enough air is used to lift the metered material and provide an adequate feed to the end distributor of a machine 30 meters in width, for example, the speed which the metered material strikes the rebound plate is so high the seed may be destroyed and the mechanical parts of the device damaged. Furthermore, this may also result in the desired amount of seed failing to fill the cross section of the feed line, and in seed accumulating in bend areas, and thus interfering with correct metering to the material.
It is therefore the purpose of the invention to provide a metering arrangement which can be used with wide machines without requiring too much air at too high a speed to deliver the metered material.